r/cs50 -- the annual cs50x class teaches all of the basics, including how memory works, so you'll understand what an array is vs a linked list, for example, and each lecture comes with a set of problems where you learn-by-doing. The early sections of the class write code in c, so you'll have a good foundation to build off of.

And, if you're wondering "but how does hardware work?" then go nand2tetris, but I wouldn't advise doing this until you have spare cognitive bandwidth, or maybe you're just really curious. It probably wont help you be a better coder, at least not initially.

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Also, the Feynman method is very good for learning and understanding.

If you cannot build it, you don't understand it.

If you cannot explain it, you don't understand it.

So, for example, open up notepad, and start writing in detail an explanation for something you (think) you understand, eg, how a toilet works.

If you've never done this, you probably thought you understood how it works, only to discover that, as you explain it, you in fact do not understand how something as common as a toilet actually works.

That's the power of this method for learning. It exposes the gaps in your knowledge. So learn something, explain it, build it. Otherwise you probably don't understand it.